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Sports injury: can athletes eat their way to recovery?
Can an athlete’s post-injury nutrition affect healing and recovery outcomes? In this two-part article, Andrew Hamilton looks at what the research says beginning with the macronutrients: protein, fats, and carbohydrates.
When injury strikes, maximizing the speed of recovery is crucial for athletes seeking a speedy return to sport. As a clinician, you will be familiar with methods such as rest, ice, stretching etc in an attempt to enhance recovery from injury. But are there any other tools that can help? In particular, is there a role for nutritional intervention? Although clinical studies are very thin on the ground, some recent research suggests that it can.
Phases of injury
Exercise-induced injuries generally have two main phases, both of which may be influenced by nutrition:
- Inflammation/ immobilization/atrophy stage (first phase)– In the initial stages, an inflammatory response is initiated, which is generally considered to be necessary for proper healing. This inflammatory stage may last for several hours up to several days depending on the injury. Depending on the type and severity of the injury, immobilization can last from a few days to several months. During this time, metabolic changes in the tissues resulting from inactivity lead to loss of strength and function (see figure 1). The loss of muscle that leads to these functional problems is well-recognized, but other tissues, such as tendon must also be considered.
- Rehabilitation and increased activity of the injured limb (second phase) – This phase follows the return of mobility leading to muscle hypertrophy and the return of functionality. Unfortunately, the complete recovery of strength and function following injury-induced immobilization takes much longer than the time it takes to lose them. In this phase, regenerating muscle tissue and consolidating the healing process (eg fracture healing, tendon repairs etc) are important.
Whereas optimum nutritional regimes may be similar for these two phases, there are some differences that may be important to consider. For example, in phase one, nutrients that can curtail excessive inflammation could, in theory, be useful. In phase two, for example, nutrients that might augment the process of knitting tendon to bone following tendon repairs could be particularly helpful. That’s the theory, but what does the evidence say?
Figure 1: Flow diagram of the metabolic and functional changes following injury-induced immobilization
Decreased synthesis of muscle and tendon proteins, as well as decreased stimulation from amino acids, leads to a quick and dramatic decrease in muscle size and strength, tendon structure and function.
NB: ‘Double down arrows’ in the boxes represent a large decrease, single down arrows represents a small decrease, single up arrows a small increase and double up arrows a large increase.
As above, while inflammation is part of the healing process, it seems sensible that avoiding excessive inflammation may be warranted. In recent years, evidence has accumulated that omega-3 polyunsaturated fats such as EPA and DHA have potent anti-inflammatory actions(1). Synergistically, EPA and DHA play a role in the resolution of inflammation through the EPA and DHA derived inflammatory mediators such as prostaglandins, leukotrienes, lipoxins, resolvins, and protectins. As well as altering eicosanoid production, omega-3 PUFAs can also reduce activation of the NF-κB pathway, reducing inflammatory cytokine production. This is in contrast to the ubiquitous omega-6 fatty acid AA, which is a known stimulator of NF-κB activity and thus pro-inflammatory(2).
So far, so good. However, the problem is that research on the necessary dose to elicit an anti-inflammatory effect in humans is still limited. One study found that the ability of EPA to reduce the pro-inflammatory hormone ‘prostaglandin E2’ occurred between an intake of 1.35 and 2.75 grams per day – much higher than that provided by most diets, even when dietary supplements are also used(3). Nevertheless, taking the evidence in the round, it seems reasonable to assume that in the acute phase following an injury, recommending that athletes increase their omega-3 intake and decrease omega-6 intake is a prudent strategy. As well as EPA/DHA supplements, this means eating more fatty fish (salmon, trout, sardines, herrings etc) flaxseed oil, walnuts, pumpkin seeds etc, while reducing intakes of omega-6 fats – commonly found in vegetable oils, such as corn and sunflower, and processed foods containing them.
During immobility, the most obvious change is a loss of muscle mass leading to reduced muscle function. Inactivity results in rapid muscle loss, and the primary metabolic factor leading to muscle loss is decreased muscle protein, particularly myofibrillar protein synthesis. Increased protein intake is often the first nutritional countermeasure considered for muscle loss. However, research shows that while protein or essential amino acid intake increases muscle protein synthesis (both at rest and following exercise), this anabolic effect is blunted during prolonged periods of immobilization (4).
One possible way around this effect is to consume protein such as whey, which is rich in the amino acid leucine. Studies in elderly humans indicate that immobilization-induced anabolic resistance may be overcome by increasing the leucine content in the diet of ingested amino acids(5). Furthermore, studies on rats in a catabolic state have shown that leucine supplementation can reverse muscle protein losses, typically increasing muscle protein synthesis back to normal levels(6). In addition, numerous other studies have demonstrated unequivocally that leucine-rich protein is superior to other proteins for stimulating the synthesis of muscle tissue.
From the above, it would seem ingesting leucine-rich protein such as whey during an initial period of immobilization following injury could be beneficial. The caveat, however, is that to date, no research has been carried out on the effects of leucine-rich protein supplementation on rates of muscle losses in injured and immobilized athletes. However, it is intriguing to consider and may well be worth a try, particularly as there is nothing to lose by experimenting. Any protein supplementation should consist of leucine-rich protein such as whey; research shows that this is more effective at promoting muscle synthesis than supplementing pure leucine as an amino acid(7).
Another important consideration during injury-induced immobilization is the total energy intake (ie calories consumed). Depending on the extent of mobilization, a substantial decrease in total energy expenditure is likely because exercise is more difficult and/or less convenient. This explains the necessity for many injured athletes to significantly reduce energy intake to avoid weight gain.
However, athletes should be cautious not to take this strategy too far. During the injury healing process, energy expenditure is increased by as much as 20%, particularly early on and if the injury is severe(8). So, whereas the total energy intake may still need to be reduced, the reduction in calorie intake may not need to be severe. There’s also the additional energy requirement for ambulation. For example, if crutches are needed, energy expenditure per unit of distance covered is typically two to three times over that of regular walking. A third caveat is that any insufficiency in energy intake will impair optimal muscle protein synthesis, in turn leading to greater muscle tissue loss. A balance, therefore, needs to be struck, but overall, a small amount of weight gain may be preferable to a lack of calorie intake to support proper muscle healing and stemming muscle protein loss.
During the rehabilitation and increased activity phase, the goal is to restore muscle mass, strength, and functionality. Other tissues affected such as tendons, ligaments and bone also need to regain maximum structural integrity, but we’ll discuss this aspect in part two.
The nutritional requirements for optimizing muscle hypertrophy during a rehab phase are similar to those above (for minimizing muscle loss). A protein intake of 2g/kg of body weight/day should be considered a minimum amount. And again, leucine-rich protein such as whey may confer additional benefits. However, with increasing activity, total energy intake will need to rise accordingly. In particular, adequate carbohydrate intake should be ensured to help fuel activity, particularly as muscle protein synthesis is an energetically expensive process, which will further increase energy requirements.
Studies on muscle damage and recovery also suggest that immediate post-exercise feeding of protein combined with carbohydrate can further enhance muscle tissue synthesis(9,10)In terms of protein quantity, a number of studies suggest that approximately 0.25 grams of high-quality protein (such as whey) per kilo of bodyweight – eg 20 grams for an 80kg athlete – is an ample amount, and around the most that can be utilized by the body after one feeding(11-13).
As for timing and frequency of ingested protein, a landmark study compared three different frequencies of whey protein feeding on recovery and muscle repair over a 12-hour period following training and an initial recovery drink(14):
- 2 x doses of 40g every six hours
- 4 x doses of 20 grams every three hours
- 8 x doses of 10 grams every 1.5 hours
Of these, it was the 20 grams every 4 hours that resulted in the greatest recovery. Of course, the 20-gram portions of protein consumed later in the day do not have to be in the form of a recovery drink – meals and snacks are fine too.
Finally, it’s worth adding that pre-sleep protein ingestion seems to significantly benefit muscle recovery and repair. One study suggests that 40 grams of casein protein before bed stimulates muscle protein synthesis overnight(15). And a recent study on subjects undergoing a 12-week training programme showed that a low-fat pre-sleep drink containing 27.5 grams of protein and 15 grams of protein boosted muscle mass and strength gains compared to no pre-bedtime drink (16).
Summary of recommendations
- During immobilization, ample energy and protein should be consumed and extra leucine intake may also be considered in an attempt to overcome this anabolic resistance.
- During rehabilitation, extra protein (particularly in association with the exercise) may increase muscle hypertrophy and speed the return to full activity.
- For optimal recovery, ample protein and energy are necessary. In particular, the timing of protein intake may help muscle protein synthesis.
- While ample omega-3 intake is desirable for limiting excessive inflammation, athletes should resist the temptation to artificially to decrease inflammation by using anti-inflammatory medication (which could be counterproductive to the healing process) unless that inflammation has been clearly diagnosed as excessive or chronic.
In part two, we’ll explore the micronutrients. Can they help speed injury healing, and which nutrients are most effective?
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